Embodiments herein generally relate to de-curling methods and devices and more particularly to those that utilize concave/convex rollers and that vary the pressure and speed between the rollers to achieve optimal de-curling performance.
Many times it is necessary to impart or remove curl from a material in order to process in the material more easily. For example, devices that transport sheets of media (such as copiers, printers, multifunction machines, etc.) often benefit from very flat de-curled sheets, which reduces the occurrence of jamming and other malfunctions. Similarly, when ribbons or webs of material are unwound from rolls, they may contain a certain amount of curl that needs to be removed.
Common devices that impart or remove curl can generally utilize pairs of rollers (note that sometimes rollers are referred to as rolls). One of the rollers is more elastic (softer) than the other roller. Pressure is applied between the rollers to form what is referred to as a “nip” and the material to be curled or de-curled is fed through the nip to have the curl removed or added.
Some forms of media can contain curl in two different directions, a lengthwise curl and a widthwise curl. This is often caused when laminated strips are stored on rolls. Such materials can have a widthwise curl caused by different coefficients of expansion of the different materials within the laminate structure. In addition, the materials can include a lengthwise curl corresponding to the curvature of the center of the roll. When media contains curls in multiple directions, conventional de-curlers need to perform multiple processes and use multiple structures to remove each of these different curls.